AIRCRAFT ENGINE SUPPORTING PYLON

STRUCTURE DE SUPPORT POUR MOTEURS D'AERONEFS

English Abstract

Pylon (19) attached to an aircraft fuselage part (17) having a close
transversal section of a curved shape comprising a skin (31) and a plurality
of
frames (33); its structural configuration comprising a central box (41) inside
the
aircraft fuselage and two external lateral boxes (51, 55) at its both sides
all of
them made with composite material, the three boxes (41, 51, 61) being
structured as multi-spar boxes with upper and lower skins (43, 45; 53, 55; 63,
65), lateral spars (47, 49; 57, 59, 67, 69) and at least a central spar (48,
58; 68);
the interface between the central box (41) and the fuselage skin (31) being
continuous; c) the pylon (19) being attached to the aircraft fuselage (17)
keeping
a full continuity in the fuselage skin (31) and a full transfer of loads
between any
interrupted intermediate frame (33') when reaching the central box (41).

French Abstract

La présente invention concerne une structure (19) de support pour moteurs d'aéronefs reliée à une section du fuselage (17) qui présente une section transversale fermée de forme courbe comprenant un revêtement (31 ) et une pluralité de couples de fuselage (33); la configuration structurale de la structure comportant un caisson central (41) à l'intérieur du fuselage et deux caissons latéraux extérieurs (51, 61) sur ses deux côtés, tous faits de matériau composite, les trois caissons (41, 51, 61 ) étant structurés comme des caissons multilongerons avec revêtements supérieurs et inférieurs (43, 45; 53, 55; 63, 65), longerons latéraux (47, 49; 57, 59, 67, 69) et au moins un longeron central (48, 58; 68); une interface entièrement continue existant entre le caisson central (41 ) et le revêtement (31 ) du fuselage. La structure est reliée au fuselage (17) de façon à assurer une totale continuité au niveau du revêtement (31 ) du fuselage et un total transfert des charges entre n'importe quel couple de fuselage discontinu (33') à la jonction avec le caisson central (41).

Claims

- 7 -
CLAIMS
1. An engine supporting pylon attached to an aircraft fuselage having a close
transversal section of a curved shape comprising a fuselage skin and a
plurality of frames, wherein:
a) the pylon comprises a central box inside the aircraft fuselage and two
external lateral boxes at both sides of the aircraft fuselage, the central
box and the two external lateral boxes being structured as multi-spar
boxes with upper and lower skins, lateral spars and at least one central
spar;
b) there is a full continuous interface between the central box and the
fuselage skin and intermediate frames interrupted by the central box; and
c) said pylon is attached to the aircraft fuselage keeping a full continuity
in the fuselage skin and a full transfer of loads between the intermediate
frames.
2. A pylon according to claim 1, wherein the central box has the same number
of
central spars as the intermediate frames, said central spars being located in
the
same fuselage section as said intermediate frames to provide them load path
continuity.
3. A pylon according to either one of claims 1 or 2, wherein said pylon
comprises
attachment means comprising:
First rows of tension fittings between, respectively, the upper and lower
skins of the two external lateral boxes and the upper and lower skins of the
central box, with first tension bolts crossing the fuselage skin; and
Second rows of tension fittings between, respectively, the lateral spars of
the
two external lateral boxes and the lateral spars of the central box, with
second tension bolts crossing the fuselage skin.

- 8 -
4. A pylon according to claim 3, wherein the attachment means also comprises
attachment fittings, with bolts between the intermediate frames and the
central
spars.
5. A pylon according to any one of claims 1-4, characterized in that said
aircraft
fuselage is an aircraft rear fuselage.
6. A pylon according to any one of claims 1-5, characterized in that the
central box
is placed within a mid fuselage section.
7. A pylon according to any one of claims 1-6 characterized in that said pylon
supports a propeller engine.
8. A pylon according to any one of claims 1-7, wherein the central box and the
two
external lateral boxes are made of composite material.

Description

CA 02787329 2012-07-16
- 1 -
AIRCRAFT ENGINE SUPPORTING PYLON
FIELD OF THE INVENTION
The present invention relates to an aircraft with propeller engines located
at its rear part and more particularly to the pylons supporting said engines.
BACKGROUND OF THE INVENTION
There are known commercial aircrafts (CBA vector 123, SARA, AVANTI,
7J7) powered with propeller engines located in the rear part of the aircraft
supported by the fuselage by means of non-moving pylons.
One of the problems raised by this aircraft configuration is related to
failure events such as a PBR ("Propeller Blade Release") i.e. an event where a
blade of one of the propeller engines comes off and hits the fuselage, a UERF
(Uncontained Engine Rotor Failure), or any other "Large Damage" event. The
design of said rear fuselage shall therefore take into account such events and
guarantee its capability for maintaining stability and proceed to a safe
landing,
i.e. shall be an impact resistant and damage tolerant fuselage.
In the prior art, non-moving pylons attached to the rear part of the aircraft
fuselage are basically made with metallic materials.
As it is well known, weight is a fundamental aspect in the aeronautic
industry and therefore there is a current trends to use composite material
instead
metallic material even for primary structures.
The composite materials that are most used in the aeronautical industry
consist of fibers or fiber bundles embedded in a matrix of thermosetting or
thermoplastic resin, in the form of a preimpregnated or "prepreg" material.
Its
main advantages refer to:
- Their high specific strength with respect to metallic materials. It is the
strength/weight equation.
- Their excellent behavior before fatigue loads.
- The possibilities of structural optimization hidden in the anisotropy of the
material and the possibility of combining fibers with different orientations,

CA 02787329 2012-07-16
2 -
allowing the design of the elements with different mechanical properties
adjusted
to the different needs in terms of applied loads.
In this framework, the present invention is addressed to the demand of
non-moving engine supporting pylons made of composite materials to be
attached to the rear part of an aircraft.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a supporting device
lo made of composite materials to be attached to an aircraft fuselage part
such as a
non-moving pylon for an aircraft with propeller engines located at its rear
part
able to withstand failure events such as a PBR or an UERF event.
This and other objects are met by a device such a pylon attached to an
aircraft fuselage part having a close transversal section of a curved shape
comprising a skin and a plurality of frames, in which:
- Its structural configuration comprises a central box inside the aircraft
fuselage and two external lateral boxes at its both sides made with composite
material, the three boxes being structured as multi-spar boxes with upper and
lower skins, lateral spars and at least a central spar.
- There is a full continuous interface between the central box and the
fuselage skin and consequently any intermediate frame is interrupted when
reaches the central box.
- The device is attached to the aircraft fuselage keeping a full continuity in
the fuselage skin and a full transfer of loads between any interrupted
intermediate frame.
In a preferred embodiment, the central box has the same number of
central spars than the number of interrupted intermediate frames, said central
spars being located in the same fuselage section that said interrupted
intermediate frames to provide them load path continuity. Hereby it is
achieved a
multi-spar pylon which is a fail safe for those considered failure events.
In another preferred embodiment, the attachment means comprise rows of
tension fittings between, respectively, the upper and lower skins of the
external

CA 02787329 2012-07-16
3 -
boxes and the upper and lower skins of the central box with tension bolts
crossing the fuselage skin; and rows of tension fittings between, respectively
the
lateral spars of the external boxes and the lateral spars of the central box
with
tension bolts crossing the fuselage skin. Hereby it is achieved an efficient
piano-
type union between the central and the lateral boxes that allows the full
continuity
of the fuselage skin.
In another preferred embodiment, the attachment means also comprise
attachment fittings with bolts between the interrupted intermediate frames and
the central spars of the central box. Hereby it is achieved an efficient union
between the central box and the interrupted frames that allows the full
transfer of
loads between them.
In another preferred embodiment, the device is a pylon located in an
aircraft rear fuselage supporting an aircraft propulsion system with propeller
blades, having the central box within the mid fuselage section.
Other characteristics and advantages of the present invention will be clear
from the following detailed description of embodiments illustrative of its
object in
relation to the attached figures.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a partial perspective view of an aircraft with a propeller
propulsion system attached to the rear fuselage through an upstream pylon
according to the present invention.
Figure 2 is a frontal view of the aircraft shown in Figure 1.
Figures 3, 4, 5 are sectional views of Figure 2 following, respectively,
planes A-A, B-B and C-C.
Figure 6 is a schematic partial perspective view of the pylon central box
showing its attachment means to the frames and to the external lateral boxes.
Figure 7 is a perspective view of an internal section of the pylon central
box, Figure 7a is enlarged view of its interface with the fuselage and Figure
7b is
an enlarged view of one of the upper zone of said interface.

CA 02787329 2012-07-16
4 -
DETAILED DESCRIPTION OF THE INVENTION
In an aircraft 11 having a propulsion system 13 with propeller blades 15
attached to the rear fuselage 17 by means of an upstream pylon 19, the rear
fuselage 17 shall be an impact resistant and damage tolerant fuselage.
The pylon 19 is a high loaded structure due to the big distance between
the propulsion means 13 and the fuselage 17. Particularly, the interface
between
the fuselage 17 and the pylon 19 is affected by high torsional and bending
moments and, in cases of crash landing and dynamic landing, to high thrust and
vertical loads. On the other hand, the pylon 19 should be a structure suitable
to
be replaced in cases of very different events such as damages due to disc
debris
events, fire, fatigue failures or engine replacements.
As illustrated in Figures 1-2, in the pylon 19 attachment zone, the rear
fuselage 17 has generally a close transversal section of a curved shape with
at
least a vertical symmetry plane D-D and a central longitudinal axis 29 and its
structure comprises a skin 31 and frames 33 dimensioned for maintaining the
aircraft stability required to proceed to an aircraft safe landing in the
event of the
release of a propeller blade 15 or any other of the above-mentioned failure
events.
Following Figures 2-5 it can be seen that in a preferred embodiment
according to the invention, the pylon 19, fully made with composite material,
comprises a central box 41 inside the aircraft fuselage 17 and two external
lateral
boxes 51, 61 at its both sides that are attached to the aircraft fuselage 17
at
medium height in a rigid manner keeping a full continuity in the fuselage skin
31.
In this respect it shall be noted that in the prior art the fuselage includes
openings
allowing the passage of the pylon supporting the propulsion system.
The three boxes 41, 51, 61 are configured as multi-spar boxes with upper
and lower skins 43, 45; 53, 55; 63, 65. Both the lateral spars 57, 59; 67, 69
and
the central spars 58; 68 of said lateral boxes 51, 61 have a C-shaped
configuration.
The lateral spars 47, 49 of the central box 41 have a C-shaped
configuration and the central spars 48 of the central box 41 have a double T-

CA 02787329 2012-07-16
-
shaped configuration (a suitable configuration for providing continuity to the
intermediate frames 33' interrupted by the central box 41).
The central box 41 is joined to the external boxes 51, 61 by means of:
- Rows of tension fittings 71 between, respectively, the upper and lower
5 skins 53, 55; 63, 65 of the external boxes 51, 61 and the upper and lower
skins
43, 45 of the central box 41 with tension bolts crossing the fuselage skin 31.
The
tension fittings 71 are connected to said upper and lower skins 53, 63, 43;
55,
65, 45 by means of shear rivets.
- Rows of tension fittings 73 between, respectively the lateral spars 57, 59;
67, 69 of the external boxes 51, 61 and the lateral spars 47, 49 of the
central box
41 with tension bolts crossing the fuselage skin 31. The tension fittings 73
are
connected to said lateral spars 57, 67, 47; 59, 69, 49 by means of shear
rivets.
The central box 41 is therefore joined to the external boxes 51, 61 by
means of a so-called piano union.
The union between the central box 41 and the intermediate frames 33'
interrupted by the pylon 19 is made as shown in Figures 7, 7a and 7b by means
of the tension and shear fitting 81 joined to the web and inner flange of the
intermediate frame 33' and the back fitting 83 joined to a central spar 48 and
to
the central box upper and lower skins 43, 45 by means of shear rivets. The
tension and shear loads are transmitted from the tension and shear fitting 81
to
the back fitting 83 by means of bolts. On the other hand the fuselage skin 31
provides continuity to the outer flange of the intermediate frame 33'.
In the embodiment just described the external boxes 51, 61 have C-
shaped spars but the skilled man will readily understand that the invention is
also
applicable to boxes with Double T-shaped spars, X-shaped spars, Double
Lambda-shaped spars, Double Pi-shaped spars, W-shaped spars, Omega-
shaped spars, or even a corrugated spar box structure.
On the other hand, it can be noted that its central spars 58, 68 does not
have any specific role in the union with the central box 41 in no-damage
conditions so that its number and position depends only on dimensioning
considerations regarding the external boxes 51, 61. In damage events, the mid
spars have the role of closing the torsion boxes.

CA 02787329 2012-07-16
6 -
Regarding the central box 41, its lateral spars 47, 49 have the same C-
shaped configuration than the lateral spars 57, 59; 67, 69 of the external
boxes.
Any other configuration of said lateral spars 47, 49 allowing a piano-type
union
such as Double T-shaped lateral spars, X-shaped lateral spars, Double Lambda-
shaped lateral spars, Double Pi-shaped lateral spars, W-shaped lateral spars,
Omega-shaped lateral spars, or even a corrugated spar box structure, will be
acceptable.
The configuration of the central spars 48 in shape and position depends
on the above-mentioned interrupted intermediate frames 33' in order to provide
the above-mentioned load transfer, that is, intermediate frames 33' load
continuity by means of said central spars 48.
It is considered that this structural design of the pylon 19 reinforces the
rear fuselage 17 torsional strength to deal with a failure event such an event
of
detachment of a propeller blade 15 from an engine 13 causing the failure of a
part of any of boxes 41, 51, 61 because the multi-spar structure of said boxes
allows maintaining a closed box to withstand the torsion moment produced in
said event.
Secondly it is considered that this structural design of the pylon 19
provides a reinforced interface with the fuselage for maintaining the aircraft
stability in any failure event.
Although the present invention has been fully described in connection with
preferred embodiments, it is evident that modifications may be introduced
within
the scope thereof, not considering this as limited by these embodiments, but
by
the contents of the following claims.

Representative Drawing